This invention relates generally to a braking control apparatus for a vehicle such as an automobile and particularly to a control apparatus whose braking force is minutely controlled electronically, and which, when slippage occurs between the wheels and the road surface, automatically performs antiskid control by suitably reducing the force acting on the wheels when the wheels lock up.
Brake fluid is discharged from the master cylinder and is supplied to the individual wheel cylinders when the brake pedal is depressed. The wheel cylinders act on the brake pistons through the hydraulic pressure of the brake fluid and the brake pistions stop the rotation of the brake discs provided concentrically to each wheel.
With this type of control apparatus, the wheels lock up when a large force is applied to the brake pedal to bring the automobile to an abrupt stop. When the wheels lock up, slippage between the wheels and the road surface occurs resulting in a loss of control and unstable operation of the automobile. Accordingly, for smooth control of the automobile it is necessary for the operator to prevent this lock up of the wheels by detecting when slippage is about to occur and then reducing the force acting on the wheels.
It is however difficult to safely control the braking force as this depends on the sensory perception of the operator. An automatic control apparatus that operates based on a running state detection signal has been strongly desired.
A conventional apparatus that has a control device for reducing the pressure of the brake fluid supplied to each wheel cylinder is well known as a means for preventing wheel lock up. When lock up is detected from the change in wheel rotation speed signal, etc., an electromagnetic valve is operated to reduce the brake fluid supplied to the wheel cylinders.
However, with this kind of control apparatus there is an increase in the piping required to supply brake fluid from the electromagnetic valve to the wheel cylinders and, because of the compressability of the brake fluid, it is necessary to control a large volume of fluid, which in turn results in the need for a large capacity electromagnetic valve and hydraulic pump. This means that the apparatus is large and complicated, and it is difficult to improve the responsiveness of the apparatus.